Direct Drive Segmented Generator

ABSTRACT

The present invention relates an electrical machine comprising a plurality of stator segments;each segment has a plurality of electrical phase windings embedded in stator slots in a phase sequence, wherein the phase of the first slot of a segment is different from the phase of the first slot of an adjacent segment.

FIELD OF THE INVENTION

The present invention relates to a direct drive generator and to asegment of a direct drive generator.

BACKGROUND OF THE INVENTION

Generators according to prior art systems typically involve one of thefollowing types of generators:

-   -   1. Conventional Wound field Synchronous Generators    -   2. Induction Generators    -   3. Permanent Magnet Generators

The main criteria used for selecting a generator to a specificapplication typically involve decisions about:

-   -   1. Torque density    -   2. Power factor    -   3. Efficiency    -   4. Weight    -   5. Cost

The above-mentioned types of generators are typically connected to a setof rotor blades through a drive-train involving a gear-box.

It may be seen as an object of embodiments of the present invention toprovide a simple and robust direct drive arrangement and avoiding thetraditional problems, such as backlashing problems, in wind turbinegearboxes.

DESCRIPTION OF THE INVENTION

This section is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This segment is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

The stator of an electrical machine normally consists of a set ofelectrical windings in which magnetic flux induces an electricalvoltage. The windings are in most machines inserted in slots in an ironcore, also known as the stator yoke. In a traditional high speedmachine, such as a or pole electrical machine, fed with a 50 or 60 Hzsupply, the stator yoke is made of a stack of lamination sheets stackedin the axial direction, each single piece of lamination circumferencethe whole rotor. Low speed machines with high number of poles and alarge diameter of several meters. For the low speed machine it ispractically impossible to make single piece of lamination, thus thestator is segmented into a plurality of stator segments.

The plurality of stator segments may form only a fraction of a statorpolygon structure. Thus, the stator segments may be arranged to coverfor example 30, 60, 90, 120 degrees (or any other angle) along thecircumferential direction of the stator. The stator segments may bearranged in a group or in groups, such groups of stator segmentsoptionally being oppositely arranged along the circumferential directionof the stator.

Alternatively, the plurality of stator segments may form a full/complete360 degrees stator polygon structure.

The stator segments may, in a radial plane of the power generator, havean essentially rectangular cross-sectional profile.

Each stator segment is preferably made of a lamination stack of thinsheet metal. Each sheet forms a two dimensional picture of a statorsegment, the third dimension is formed by the stacking of the laminationsheets. The sheets are formed so that there are slots for receiving anumber of stator winding, one can also say that the slots form a numberof stator teeth. The stator segment then has a first side formed by thefirst piece of lamination sheet, and a second side formed by last pieceof lamination sheet. The other four sides comprise the main sides of thelamination sheet and are thus: a front side (facing the air gap), a rearside opposite of the air gap that should face the rotor of the machineand the remaining two sides that will be adjacent to the adjacentsegment.

Each stator segment may comprise a dovetail shaped attaching arrangementfor securing each stator segment to a frame structure. The dovetailshape may be positioned on the rear side of the segment. A non-magneticmaterial may be positioned between the dovetail shaped attachingarrangements and the frame structure in order to reduce leakage fluxbetween stator segments and the frame structure. The non-magneticmaterial may comprise a stainless steel cover positioned between thedovetail shaped attaching arrangements and the frame structure.

V-shaped gaps may exist between neighbouring stator segments when theseare aligned in the polygon structure. A ferromagnetic material may beposition in the V-shaped gaps between neighbouring stator segmentsthereby enhancing the efficiency of the power generator. Moreover,suitable stator cooling means may be positioned within the V-shapedgaps.

Each stator segment may comprise steel laminates, said steel laminatesbeing arranged in a tangential direction to the circumferentialdirection of the stator.

In a first aspect, the present invention relates to an electricalmachine comprising a plurality of stator segments, each segment has aplurality of electrical phase windings embedded in stator slots in aphase sequence, wherein the phase of the first slot of a segment isdifferent from the phase of the first slot of an adjacent segment.

An advantage of this aspect is that the voltage induced in the phasesgets more even and with lower harmonic content, and effects from leakageflux in the end of the segments are also reduced.

According to one embodiment of the invention an electrical machinewherein the sequence of the phase windings is so that the phase windingsform a plurality of electrical phases distributed equally with the samephase angle between the electrical phases.

An advantage of this aspect is that the overall picture of the voltagesfrom the electrical phases causes an even lower harmonic content.

According to one embodiment of the invention each of the phase windingsin each segment is connected in series with the phase winding of acorresponding electrical phase in the adjacent segment.

An advantage of this aspect is that the electrical phase gets voltagecontribution from more segments. The contribution from each segmentmight not be the same, but when added together the electrical phases arebalanced.

According to one embodiment of the invention herein the number ofwindings connected in series equals the number of phase windings in eachsegment times N, wherein N is an integer.

An advantage of this aspect is that the electrical phase gets voltagecontribution from more segments. The contribution from each segmentmight not be the same, but when added together the electrical phases arebalanced and with this embodiment each electrical phase getscontributions from each location in the segment and thus the voltagesare as balanced as they can get.

According to one embodiment of the invention, the length of at least oneof windings in a segment differs from the length of the other windings.

An advantage of this aspect is that it is not critical if one of thewindings is longer than the others and therefore does the winding layoutnot have to be so each winding have the same length.

According to one embodiment of the invention the electrical machine hasP segments that form a first set of electrical phases and Q segmentsthat form a second set of electrical phases, the phases of the first setis not aligned with the phases of the second set of electrical phases,wherein P and Q are an integer.

An advantage of this embodiment is that the machine can operate with twosets of electrical phase, when both sets are operating they causes lessharmonics, due to the higher number of phases.

According to one embodiment of the invention, the electrical machine haswindings which are a concentrated wound winding around a single statortooth of the segment.

An advantage of this embodiment is that the filling factor of slotsmight be higher than for other winding configurations, and that thewindings itself is easier to manufacture and to insert.

A second aspect, the present invention relates to a method of assemblingan electrical machine comprising a plurality of adjacent statorsegments, each segment comprising a yoke with a plurality of statorslots, said method comprising the steps of:

-   -   in a first segment, embedding a plurality of electrical phase        windings in the stator slots in a phase sequence;    -   in an adjacent segment, embedding a plurality of electrical        phase windings in the stator slots in a phase sequence,    -   connecting the phase windings in the first segment in series        with the phase winding of a corresponding electrical phase of        the adjacent segment so that the phase of the first slot of a        segment is different from the phase of the first slot of an        adjacent segment.

The advantages of the second aspect are equivalent to the advantages forthe first aspect of the present invention.

Many of the attendant features will be more readily appreciated as thesame become better understood by reference to the following detaileddescription considered in connection with the accompanying drawings. Thepreferred features may be combined as appropriate, as would be apparentto a skilled person, and may be combined with any of the aspects of theinvention.

The present invention will now be explained in further details. Whilethe invention is susceptible to various modifications and alternativeforms, specific embodiments have been disclosed by way of examples. Itshould be understood, however, that the invention is not intended to belimited to the particular forms disclosed. Rather, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in further details withreference to the accompanying figures, wherein

FIG. 1 shows an embodiment with tapered stator segments,

FIG. 2 shows an embodiment with rectangular stator segments,

FIG. 3 shows rectangular-shaped stator segments,

FIG. 4 shows V-shaped gaps 6 between stator segments,

FIG. 5 shows a partial stator arrangement,

FIG. 6 shows a partial stator arrangement without V-shaped gaps,

FIG. 7 shows a tapered stator segment,

FIG. 8 shows adjacently arranged stator segments with open V-gaps,

FIG. 9 shows adjacently arranged stator segments with filled V-gaps,

FIG. 10 shows a Dash type Inductor alternator (prior art),

FIG. 11 shows a double stator/single rotor Axial flux Dash typegenerator,

FIG. 12 shows a double stator/single rotor radial flux configuration,

FIG. 13 shows an Arc-shaped machine,

FIG. 14 shows a double stator/double rotor arrangement in an axialconfiguration,

FIG. 15 shows a single stator/single rotor Lorenz machine with permanentmagnet excitation,

FIG. 16 shows a double stator/single rotor configuration with permanentmagnet excitation,

FIG. 17 shows a double stator/single rotor with DC current excited coilsin the stator,

FIG. 18 shows a concentrated phase and field winding,

FIG. 19 shows a Linear Hybrid Synchronous Motor,

FIG. 20 shows a double-sided stator of a Linear Hybrid SynchronousMotor,

FIG. 21 shows a cylindrical radial flux Hybrid Synchronous Motor,

FIG. 22 shows a double sided axial flux Hybrid Synchronous generator,

FIG. 23, Single layer multi level phase winding and gramme ring windingfor DC excitation,

FIG. 24 shows a fault tolerant phase winding,

FIG. 25 shows slots of the same size for phase winding and DC excitedfield winding,

FIG. 26 shows a modified E-core arrangement with deep field coils,

FIG. 27 shows a half model of a stator, a rotor and permanent magnetarrangement (4 pole model),

FIG. 28 shows a hybrid synchronous machine with gaps in magnets,

FIG. 29 shows a hybrid synchronous machine with magnets embedded in theslots 2,

FIG. 30 shows a polygon-shaped hybrid synchronous machine,

FIG. 31 shows torque ripple reduction,

FIG. 32 illustrate force ripples for various cases,

FIG. 33 shows a segment of a machine with DC winding inserted in theslots 2, can be used for magnetic bearing operation.

FIG. 34, shows a segment of a machine with DC winding where the DCcurrent direction in the air gap control winding for a given excentricrotor position

FIG. 35 shows a segment of a machine with single layer windings.

FIG. 36 shows two adjacent segments of a machine with single layerwindings, and where the end tooth of each segment has the half width.

FIG. 37 shows a segment of a machine with a double layer windingsconfiguration, with lap windings.

FIG. 38 shows a segment and part of adjacent segments of a machine witha double layer windings configuration, with lap windings, with the lastwinding around the end tooth.

FIG. 39 top: shows a segment and part of adjacent segments of a machinewith a double layer windings configuration, with lap windings, with thelast winding around the end tooth.

FIG. 39 bottom shows a segment and part of adjacent segments of amachine with a double layer windings configuration, with lap windings.

FIG. 40 a shows a segments and part of adjacent segments of a machinewith a concentrated windings single layer configuration.

FIG. 40 b shows a segments and part of adjacent segments of a machinewith a concentrated windings double layer configuration.

FIG. 41 shows the winding path of a segment of a machine, with large endwinding waste and pluralities of triple winding overlaps.

FIG. 42 shows the winding path of a segment of a machine, with large endwinding waste and pluralities of triple winding overlaps.

FIG. 43 shows the winding path of a segment of a machine with optimalwinding configuration, with low end winding waste.

FIG. 44 shows the winding path with turns of a segment of a machine,with large end winding waste.

FIG. 45 shows the winding path with turns of a segment of a machine,with low end winding waste.

DETAILED DESCRIPTION OF THE INVENTION

Polygon Shaped Machine

In its most general aspect the present invention relates to a newconfiguration of a stator for an axial flux machine. This novel machineconfiguration can be produced cheaper compared to traditional machineconfigurations.

Referring now to FIG. 1, in axial flux machines the lamination directionhas to be in the tangential direction. Hence the lamination has to havea curvature. Because the circumference of the whole machine increaseswith increasing radius each lamination layer has to be a little larger.Thus, the positions of all the slots 2 at each single lamination layerneed to be adjusted dependent on the lamination layer number.Fabricating axial flux machine stator with slots 2 is therefore acumbersome process due to direction of the lamination.

The present invention relates to a stator arrangement where arectangular block is made using thin steel laminates 4 similar totransformer E cores or linear machine lamination processes. A typicalstator yoke block is shown in FIG. 3. The direction of lamination 4 isdepicted in FIG. 2.

If a very large mean diameter (>3 m) for the axial flux machinecomprises a high number of slots 2 (>72), and if the iron length incomparison to the mean diameter is small (<0.5 m) the fabrication can besimplified a lot without significant disadvantages.

The stator has to be divided into many segments 3. Each segment 3contains a low number of slots 2 (e.g. 6 slots). Each segment 3 has thesame shape and it can be fabricated by stacking together just one shapeof lamination. The tooth 24, 25 length is constant. All these segments 3have to be put on a polygon structure. Finally, a stator 1 can beassembled that looks fairly similar to the conventional. The onlydifference is small V-Gaps 6 (Gap distance <2 mm).

The big advantage is that the amount of different parts is very lowcompared to conventional stator designs.

The new stator design applies to axial flux machines with largediameters and relatively low iron length.

FIG. 4 and FIG. 5 show arrangements of axial flux topology withrectangular blocks. This arrangement results in a plurality of V gaps 6between adjacent segment 3 b and results in loss of power production.

It has been found that the filling up V gap 6 with ferromagneticmaterial 7 helps increasing the produced power by 20%. Having smallconstant air gap (inner to outer radius) say 1 to 2 mm between segments3 does not decrease significantly power out of the machine. A typicalarrangement without V gap 6 is shown in FIG. 6.

FIG. 7 shows lamination stack that helps keeping equal air gap betweenthe segments 3. Here are the ends of each segment 3 tapered 8 b byremoving a triangle of the lamination stack 4. This tooling processneeds to ensure that it will not cause too many short circuits for eddycurrents.

Depending on the chosen winding configuration these V-Gaps 6, cf. FIG.8, are decreasing the flux density in the air gap. In such a case theGap 6 should be filled up, cf. FIG. 9, with some iron material 7 toclose the magnetic circuit. The filling material 7 may be of a sintermetal type with high permeability.

Studies have shown that filing in the triangle gives up to 20% morepower output.

The reduction in force density using the polygonal form of the machineis significant. This is due to the following:

-   -   1. The introduction of gaps 6 in the backing iron disrupting the        normal flux pattern,    -   2. The distortion of the slot pitch (distance from slot to slot)        giving rise to uneven phase sequence in the machine which gets        worse at the outer radius.

Item 2 is inherent in using parallel slot/parallel tooth segments 3 foran axial flux machine, and can only be mitigated by using the smallestradial length possible. However, item 1 may be reduced if the segments 3are manufactured from laminations of the length commensurate with theouter radius, and then given the appropriate taper 8 b on the sidesafter assembly into a segment 3, possibly by the use of water-abrasivejet. This will allow the segments 3 to be packed together as a series ofsegments without undue gaps 6 in the backing iron, cf. FIG. 1.

It is clear that the disruption of the normal backing iron flux patternby introducing an inter-segment 3 gap is responsible for the majority ofthe loss of performance of the polygonal version of this machine.

In all these models, no account has been taken for stator laminationmaterial that will be needed to support the stator within the structure.Because of the very high flux loading of the material, it will not bepossible to use the usual expediency of drilling holes in the backingiron for mounting purposes, as this will reduce the performance of themachine. Instead, additional material will be needed behind the existingbacking iron, with appropriate shapes for support purposes. This maytake the form of dovetails to allow the laminations to be wedged into asupport structure, or a series of tabs with holes in, that may beselectively removed to provide support along the radial direction withthe through bars engaging on sleeves in the support structure.Alternatively, the backing iron depth may be increased in depth by thediameter of any holes drilled: but this method does not provide supportin the middle of the stack without additional internal structures.

The lamination stacks with a dovetail on the back for connectionpurposes may in order to avoid leakage flux have an air gap between thesupport structure and corresponding dovetail, the air gap can be filledwith non magnetic material, plastic, stainless steel etc. to limitleakage flux.

The space of the V-Gap 6 can also be used to bring some cooling liquidclose to the stator.

In case there need to be an air gap bearing to control the air gap, theV-Gap 6 could be used to put some superconductor inside. In case thesuperconductor becomes superconducting, the Meisner Effect will occur inbetween the magnets and the superconductor and act as an air gapbearing. Because of the alternating magnetising direction of themagnets, there might be some losses in the superconductor that have tobe taken out. The size of the V-Gap probably needs to be increased tohave enough space for the superconductor including thermal insulation.

The concept of the polygon axial flux machine is not limited the typesof machines described else where in this application. It would also beadvantageous to apply the polygon concept to a traditional PermanentMagnet (PM) axial flux electrical machine.

Direct Drive (Gear less) wind drive train for which the before mentionedpolygon generator design is suitable for, is often designed in an axialflux or radial flux type of machine.

-   -   6. The electrical machine or generator that will be described in        the following will all be possible to make in a polygon form if        it is a design with axial flux. On the other hand it is also        possible to make them in a radial flux design, thus without the        polygon design.

In the following three different concepts of electrical generators for awind turbine generator will be presented, common for all of them is thatthey have a rotor that does not consist of permanent magnetic materialand it does not have any rotor windings, as known from synchronous orinduction generator. The magnetic flux in the machines is produced fromvarious sources in the stator.

The rotor of the three different machines can be made with a combinationof magnetic material and none-magnetic material in order to generatereluctance in the magnetic field. Alternatively, the rotor may be ametal disc (may be magnetic material) with protruding magnetic material.None of them have permanent magnetic materials in the rotor.

Although they are all mainly shown in an axial flux type embodiment manyof the advantages would also apply to a radial flux type machine, andthus many aspects of the application should not be limited to an axialflux electrical generator.

Focus will be on PM less type generators which can be employed in windgenerators having diameters larger than 5 m and less than 30 m, but notlimited to that range.

Dash Electrical Generator

Dash proposed an inductor type generator which can be adopted as agenerator in wind turbine generators.

The schematic diagram of Dash concept is shown in FIG. 10. This is aradial flux cylindrical type machine.

The stator consists of symmetrical slots 2 in which phase and fieldwindings are placed as shown in FIG. 10. Field windings are labeled as1′, 2′, 3′, 4′, 5′, 6′ & phase windings are labeled as 1, 2, 3 ,4, 5, 6.

The rotor consists of several teeth made of ferromagnetic material. Whenthe rotor revolves in the magnetic field set up by the field winding,the magnetic field is modulated and voltage is induced in the stator.

The main advantages of Dash type generators are:

-   -   1. Simple rotor structure that enables to go for very large        diameter generators.    -   2. Stator can be segmented in to many parts that help to realize        a modular type generator concept.    -   3. Stator can be 360 mechanical degrees and it can be an arc        shaped having N mechanical degrees    -   4. Faulty segments can be disabled easily by switching off the        corresponding field winding or the faulty segments 3 can be        removed physically while the generator is in operation    -   5. Highly suitable for off-shore/on-shore as maintenance free        type    -   6. This machine can be configured as axial or radial flux        machine    -   7. The machine can be designed with multiple air gap or        multi-stack features for adding power output levels.    -   8. It is highly suitable for concentrated phase winding 23 a, 23        b, 23 c type machine.

Teeth Combination of Stator/Rotor:

Prior art has demonstrated working principle using 12 stator teeth and 7rotor teeth. However, the inventors optimization work shows thatgenerators with 12 stator teeth and 5 rotor teeth develop approximately36% higher force density compared to the prior art 12/7 combination.

A typical double stator/single rotor axial flux Dash type generator isshown in FIG. 11, whereas FIG. 12 shows a radial flux doublestator/single stator configuration.

A typical arc-shaped generator is shown in FIG. 13. The advantages ofthis arc type machine is that the stator may not have to circumferencethe rotor all 360 degrees, meaning that one rotor diameter can fit toseveral power ranges, depending on the number stator segments 3attached. The stator segments 3 can be located in one group or in two ormore groups, preferable with one group of stator segments 3 in thebottom and one in the top of the generator.

Lorentz Electrical Generator

For large diameters (>5 m) the Lorenz generator can be used. The rotorconsists of blocks of ferromagnetic steel followed by none magneticblocks whereas the stator consists of windings inserted slots 2 andpermanent magnets on the stator for excitation.

The permanent magnet may be replaced by dc current windings that can beplaced in the slots 2.

This machine may be configured in axial or radial flux configuration.

a) Axial Flux:

-   -   1. Double sided stator/single rotor    -   2. Single stator/double rotor

b) Radial Flux:

-   -   1. Double sided stator/single rotor    -   2. Single stator/double rotor

The Lorenz machine can be realized with

-   -   1. Full laminated stator (360 deg) or sector of n deg    -   2. N number of segmented stator for 360 deg or n deg

Axial Flux Double Stator—Double Rotor Arrangement:

To the above concept, magnetic bearing effect can also be incorporatedif the magnetic set up by stator 1 and stator 2 linked with rotor 1 androtor 2 respectively.

Possible stator/rotor configurations are shown in the following figures,where FIG. 14 shows a double stator/double rotor arrangement in an axialconfiguration, FIG. 15 shows single stator/single rotor Lorentz machinewith permanent magnet excitation, FIG. 16 shows a double stator/singlerotor configuration with permanent magnet excitation, FIG. 17 shows twoadjacent stator segment 3 b/single rotor with DC current excitation andFIG. 18 shows a concentrated phase and field winding.

Hybrid Synchronous Machine (HSM)

The “HSM” machine differs from the “DASH” machine primarily by havingpermanent magnets with alternating magnetic poles on the stator surface.

The basic hybrid synchronous machine topology is shown in FIG. 19. Themachine consists of stator with winding and a salient pole reluctancerotor. Permanent magnets are placed on the stator teeth as shown in theFIG. 19. The PM sets up a magnetic field and links with stator windingand the magnetic reluctance rotor.

In generator mode, the magnetic flux linkage with the winding varieswhen reluctance rotors moves and hence the voltage gets induced.

The developed torque is expressed as;

$T = {\frac{gP}{\omega_{s}} = \frac{3\; {gpVE}\; \sin \; \delta}{2\pi \; {fX}}}$

Where,

V=Terminal Voltage

E=Induced Voltage

f=frequency of voltage

X=reactance of the stator winding

g=gear ratio=rotor speed/primary travelling field speed

p=number of rotor segments/winding pole pair

Variants of HSM are shown in FIGS. 20-26. A double stator hybridsynchronous machine topology is shown in FIG. 20. FIG. 21 shows athree-dimensional view of a single stator HSM, whereas FIG. 22 shows athree-dimensional view of a double stator HSM. FIG. 23 shows anillustration of the positioning of the three phase windings red (R),yellow (Y) and blue (B). FIG. 24 shows the positioning of the phasewindings (R), (Y) and (B) in the stator, and their relative positions tothe field windings and the rotor blocks. FIG. 25 illustrates varioustypes of stator layouts, whereas FIG. 26 illustrates two E-core statorarrangements.

The HSM can be used as generator for diameters >5 m. When the diameterof the machine is >5 m the stator can be segmented. The generator can bea segmented radial or axial flux type generator. The number of segmentscan be selected based on the weight and power consideration.

A typical generator with double layer winding stator is shown in FIG.27. The air gap between the magnets and the stator teeth is zero.

A small air gap between the magnets and gap (<1 mm) between the statorteeth and the magnets (<0.5 mm) do not change the power significantly. Atypical arrangement of the stator and the rotor is shown in FIG. 28.

Magnets can be embedded inside slots 2 as shown in the FIG. 29. Thishelps retaining the magnets on the stator teeth. This arrangement doesnot increase the magnet leakage flux and does not significantly decreasethe power level.

A HSM can be configured and shaped, cf. FIG. 30, as a polygonal statorwith stator winding having double layer stator.

A torque ripple reduction techniques in a segmented stator with HSM usedin wind turbine application has been analyzed.

The V-gaps 6 between adjacent stator segments 3 b result in entry andexit magnetic field effects and its associated problems such as forceripples, a technique is proposed for reducing torque ripple to 50%. Thisincludes:

Step 1: Adjust the gap between the stator segments 3 in terms of numberof rotor segments

Step 2: Reverse the phase currents with respect to adjacent segment 3 bphase currents.

Typical arrangement for 3 cases is shown in FIG. 31 and the resultingforce ripples curves are shown in FIG. 32.

Ripples in tractive and normal force in polygon shaped HSM can bereduced by suitable spacing of the adjacent stator segments 3 b withrespect to the number rotor segments that cover the entire stator lengthand by reversing the phase of currents of adjacent segment 3 b withrespect to the other segment 3.

Air gap control may apply to all types of machines mentioned here.Control of magnetic bearing may be very simple without additionalsensors—for example by comparing the voltage induced in the stator coilson each side. Based on the result of such a comparison it is clear onwhich side the air gap needs to be adjusted.

Direct Drive machines of MW rating require very narrow air gap (of theorder of a few mm, less than 10 mm) and large diameter (>5 m & <30 m) inorder to reduce active mass.

Maintaining very narrow air gaps in such large diameter machines are achallenging mechanical design problem. Hence, these kinds of machinesrequire local air gap control.

Local air gap control can be realized by means of mechanical contactbearing or fluid bearings or contactless magnetic bearing.

A separate 5 axis magnetic bearings can be added along with generator.This idea increases weight of the generator system.

According to the present invention additional windings may beincorporated in the stator (single side of double sided machine) asshown in FIG. 33. The air gap between the stator and the rotor can bemaintained by changing dc current by sensing the rotor position.

An additional winding in the stator slot 2 with dc excitation canproduce bearing action in order to control the air gap. The performanceof the machine and the weight of the machine is not affectedsignificantly by the additional winding. Nor is the performance of themachine in terms of power factor and losses affected.

An embodiment of the present invention relates to the electrical phasewindings of the stator. All embodiments have a stator consisting ofsegments that are put together to form the stator as shown in FIG. 4 orFIG. 5. This may relate to an axial flux machine where the magnetic fluxis parallel to the rotating shaft of the machine or to a radial fluxmachine where the flux is perpendicular to the rotating shaft of themachine.

In some embodiment the stator is 360 degrees (FIG. 4), in otherembodiments the stator is limited one or more areas of for example 60degrees (FIG. 5). Common for most embodiments is that the statorconsists of segments.

Each stator segment 3 may comprise a dovetail shaped attachingarrangement for securing each stator segment 3 to a frame structure. Thedovetail shape may be positioned on the back side of the segment. Anon-magnetic material may be positioned between the dovetail shapedattaching arrangements and the frame structure in order to reduceleakage flux between stator segments and the frame structure. Thenon-magnetic material may comprise a stainless steel cover positionedbetween the dovetail shaped attaching arrangements and the framestructure.

V-shaped gaps 6 may exist between neighbouring stator segments whenthese are aligned in the polygon structure. A ferromagnetic material maybe position in the V-shaped gaps 6 between neighbouring stator segmentsthereby enhancing the efficiency of the power generator. Moreover,suitable stator cooling means may be positioned within the V-shapedgaps.

Each stator segment 3 may comprise steel laminates 4, said steellaminates 4 being arranged in a tangential direction to thecircumferential direction of the stator.

Each stator segment 3 is preferably made of a lamination stack of thinsheet metal. Each sheet forms a 2 dimensional picture of a statorsegment, the third dimension is formed by the stacking. The sheets areformed so that there are slots 2 for receiving a number of statorwinding, one can also say that the slots 2 form a number of statorteeth. The stator segment 3 then has a first side 14 formed by the firstpiece of lamination sheet, and a second side formed by last piece oflamination sheet. The other four sides comprise the main sides of thelamination sheet and is thus: a front side (facing the air gap), a rearside opposite of the air gap, see FIG. 3 and the remaining two sidesthat will be adjacent to the adjacent segment 3 b.

All electrical three phase system, but also electrical systems of highernumber of phases, can be connected in various ways. The two most commonsystems for a three phase setup are the Delta coupling and the Wyecoupling. An electrical machine coupled in a Wye need to have one end ofeach of the three phase windings of the machine connected to a commonpoint.

A segment 3 for an electrical machine according to any of theembodiments, should either by connected in Delta, Wye or with openwindings. In case of open windings, the windings can connected at acommon bus connector or alternatively can a groups of segments beconnected into serial segments, wherein for the serial segments, each ofthe plurality of windings is connected in series with its correspondingwinding in the adjacent segment 3 b, and wherein the plurality of endingpoints is connected at a common point, the star point. The correspondingwinding in the adjacent segment 3 b is normally the winding which has aphase voltage that is in phase with the phase voltage of the segment.There may be situations where they are not in complete phase with eachother.

In radial a flux machine the stator lamination is stacked in the axialdirection and the axial flux machine is stacked in the tangentialdirection, see FIG. 1 and FIG. 2.

In the embodiments of the axial flux machine, each segment 3 is actinglike a single linear machine, magnetic decupled from the other segmentsthrough a gap. The segments should be as close as possible to each otherso that the distance/gap between adjacent segments 3 b is low. This is,because all magnets in front of such a distance/gap do not create anytorque, hence they are useless. The stator lamination stack of a radialflux machine can be made so there is virtually no gap between thesegments.

For the axial flux the amount of these useless magnets can be reduced,if the distance/gap between is reduced as well.

The winding 20 a, 20 b, 20 c, 21 a, 21 b, 21 c can be made in a singlelayer configuration or a two layer configuration, or even with morelayers.

The windings of a segmented machine can either be a concentrated winding23 a, 23 b, 23 c, as shown in FIG. 40 or a lap winding, as in FIG. 35.

The concentrated winding configuration is where each of the windings 23a, 23 b, 23 c is a concentrated wound winding around a single statortooth 24, 25 of the segment. In FIG. 40 the windings are in two layers,a similar configuration can also be made for a machine with single layerconcentrated windings 23 a, 23 b, 23 c, where only one phase windingwill be in each slot.

The lap winding configuration is as shown in FIG. 35. Each of the phasewindings is wound with one or more turns that go around more than onestator tooth 24, and where the next phase winding is in the adjacentslot 2 with turns that goes around the same number of slots 2 as theearlier mentioned phase winding. The phase windings are leaping eachother. The phase winding may consist of one or more sectors of thewinding where each sector is a number of winding turns around the sameslots 2. The next sector of the first phase winding is wound around anew group of slot 2 after the last phase winding. FIG. 36 shows twoadjacent segments 3 b where each segment 3 contains a three phasewindings (v, u, w) 20 a, 20 b, 20 c in a single layer, each segment 3only have one winding sector. The plus and minus indicates the directionof the winding in the slot.

FIG. 35 shows more than two segments where each phase winding 20 a, 20b, 20 c consist of two sectors in a single layer. FIG. 37 shows asegment 3 with a two layer lap winding, the winding in the left mostslot 27 “−v” starts in the bottom layer 21 a and goes around threestator tooth 24, 25 and is in the fourth slot 28 as the “+v” winding inthe upper layer 22 a, the same applies to the “u” and “w” winding.

The winding may be embedded in the slots 2 in a single Layer Lap Winding20 a, 20 b, 20 c meaning that all teeth are filled up with a oneconductor. Between two segments there is a V-gap in the size of ⅓ of apole pitch at the medium diameter. The phases are distributed in thesegments differently, so that all phases are present at the first slot 2and last slot 2 of a segment 3 the same number of times.

In an embodiment of the present invention, an electrical machinecomprising a plurality of stator segments, where each segment 3 has aplurality of electrical phase windings embedded in stator slots 2 in aphase sequence, and wherein the phase of the first slot 2 of a segment 3is different from the phase of the first slot 2 of an adjacent segment 3b. Meaning that the sequence of the phases might be same, but the orderof which they start in the first slot 2 differs.

The sequence of the phase windings in the electrical machine is so thatthe phase windings form a plurality of electrical phases distributedequally with the same phase angle between the electrical phases. For athree phase machine there should be angle of 120 electrical degreesbetween the phases.

The location of the individual phase in the segment 3 may affect thevoltage level induced in the winding, therefore the voltage level of thethree phases is not fully balanced. This may come from the fact that thelength of at least one of windings 20, 21, 31 in a segment 3 differsfrom the length of the other windings in the same segment, which againmight be related to the specific location of the winding in the slot 2and the distance to the star point 39 and/or distance to terminal box orterminal bus bar, where the winding ends 40, 41 are connected in orderto reach the electrical connection to the electrical grid or like wherethe machine is to be connected.

Changing the order of the phases for balancing the voltages of a largerpart of the machine is a solution to overcome that problem, as anexample three segments 3 can be connected in series, where each of thephase windings 20, 21, 31 in each segment 3 is connected in series withthe phase winding of a corresponding electrical phase in the adjacentsegment 3 b.

For an electrical machine of the present invention the number ofwindings connected in series should equals the number of phase windingsin each segment 3 times N, wherein N is an integer. This means that fora 3 phase machine the number of segment 3 should be 3, 6, 9 . . . etc.

In one embodiment of the invention an electrical machine is having twoset of a plurality of phases, and where P segments form a first set ofelectrical phases and Q segments form a second set of electrical phases,the phases of the first set may not be aligned with the phases of thesecond set of electrical phases, wherein P and Q are an integer. In anexample a machine is having 2×3 phases with a phase displacement of 30electrical degrees.

In a single layer winding configuration, the windings can be put intothe segments as shown in the FIG. 35 In this version a full tooth 25 isused at the end of the segment. Here the whole slot 2 width is used as adistance between the segments 3. In one implementation is the yokeheight increased a bit to avoid that a big amount of flux jumps from onesegment 3 to the next.

The configuration of FIG. 36 is a configuration with single layerwinding 20 a, 20 b, 20 c, like in FIG. 35, but the where last statortooth 25 is only of half the width, i.e. a half tooth 25. In this caseit can be put into the segments as shown in FIG. 36. Here the segment 3is ended with a half tooth 25. The distance between these segments needto be kept very small; to ensure that not too much of tooth width islost. It might be necessary to increase the Yoke height a bit to avoidthat a big amount of flux jumps from one segment 3 to the next.

An end tooth 25 at the end is necessary to take all the flux that cannot go to the next segment. It can not be removed, without decreasingthe power. Hence a quite large V-gap 6 of ⅓ of a poles pitch isnecessary.

For a Double Layer Lap Winding as shown in FIG. 37 where the segmentsare ended with a half tooth 25. The distance between these segments needto be kept very small; to ensure that not too much of tooth width islost. At the end of each segment 3 the slots 2 are just filled up withone layer, this helps that the flux density goes down. Hence the Yokeheight doesn't need to be increased.

In another embodiment a Full tooth 25 is at segment 3 end, as in FIG. 35or in the lower figure of FIG. 39.

The use of single or double layer can be mixed with all embodimentsmentioned in this application.

A way to reduce the gap between to segments is to eliminate the lastslot 2 and moving the two segments closer together. By this the V-gap 6size will be reduced. The two coils, which are now outside of thesegment, can overlap, because it is a bottom layer and a top layer. Inorder to ensure that the top layer stays as a top layer, before assemblyof the machine a non-magnetic spacer (not shown) can be inserted in thelast stator slot 2 under the top layer, by doing so the winding maintainits position, and will not block for the bottom layer winding of theadjacent segment 3 b.

The benefit of this invention is that the amount of magnets per Torquecan be reduced. Also torque ripple will be reduced, because the teethfor different segments do affect the poles differently for the samerotor position.

The lower figure of FIG. 39 shows segment 3 where the teeth 25 at theend of the segments are just half filled up with a conductor with doublelayer lap windings. The upper figure of FIG. 39 also shows a segment 3where the teeth at the end of the segments are just half filled up witha conductor with double layer lap windings, but without the last tooth25. This also applies to FIG. 38 showing two segments with a V-gap inthe size of ⅙ of a pole pitch at the medium diameter.

In an embodiment the segment 3 can have a higher number of slots 2, andthus the width also tend to be larger (covering a larger number ofangular degrees by the segment), and by this the total segment 3 numberis lower, in order to avoid having too many half filled slots 2.

In FIG. 38 is the V-Gap 6 between the segments is smaller, because theend tooth 25 is missing. Therefore many teeth are only filled half. Thisreduces the power almost similar as for the single layer classicalwinding 21 a, 21 b, 21 c. An advantage of this is the slightly simplerand shorter end winding compare to the single layer winding 20 a, 20 b,20 c.

Finally at the two ends the last three slots 2 are only half filled.Hence the created torque from this segment 3 is only half. The idea isto eliminate the last tooth 25. By this, one coil (either the bottomlayer or the top layer) is outside of the segment. Now the two segmentscan be moved very close to each other. At the V-Gap a bottom layer willmeet a top layer coil. Finally they will be one after another.Overlapping does not take place. A segmented axial flux machine, thathas a two layer lap winding. Between the layers there is a V-Gap 6. Thelast three slots 2 are only filled half with copper.

A method to increase the so called Carter factor in a machine withconcentrated winding 23 a, 23 b, 23 c is by having a forked slot,meaning that an additional pole piece is introduced in between the twosets of windings in each slot 2 in FIG. 18.

The Carters Factor will be higher with such a forked slot. A higherCarters factor means that the flux density in the air gap is higher.Finally more torque can be produced.

In one configuration the phases of two segments, which are adjacent toeach other, but located at different places, these can be connected inseries together. This is possible if the distance in between twosegments is e.g. ⅓ or ⅔ of a pole pitch instead of 3/3 of a pole pitch,other ratios may also apply. If the phases of three segments, that arenext to each other are connected to each other in series, the terminalvoltage, which is the sum of all the three different characteristics ofthe segment 3 voltages, is the same for all phases. Finally the Voltageis balanced in all the phases. This means three segments are puttogether and become an independent system, with a balance phases. Thethree segments cannot be operated independent to each other any more.Similar can be made for machine with higher number phase, such asmultiple of 3, or any other combination.

Although the previous paragraph mentioned that the serial connection ofsegments should be with adjacent segments 3 b, similar serial connectionwill also work between segments that are not adjacent to each other.

The three voltages of the three phases of a stator segment 3 do not havethe same amplitude and harmonics. This is because each phase is locatedat a different location in the segment 3, than another phase. Thus thesystem is not symmetric for all the three phases.

The present invention also relates to a method of assembling anelectrical machine with a plurality of adjacent stator segments 3, eachsegment 3 comprising a yoke with a plurality of stator slots 2, themethod comprising the steps of: In a first segment, embedding aplurality of electrical phase windings in the stator slots 2 in a phasesequence; In an adjacent segment, embedding a plurality of electricalphase windings in the stator slots 2 in a phase sequence. The phasewindings in the first segment 3 is to be connected in series with thephase winding of a corresponding electrical phase of the adjacentsegment, so that the phase of the first slot 2 of a segment 3 isdifferent from the phase of the first slot 2 of an adjacent segment.

When arranging the phase windings in the slots 2 of the stator 1 manyissues have to be considered. One thing that is important is to make themost optimal use of the length of the winding 20. There is only inducedvoltage in the winding where ever the winding is exposed to a change inthe magnetic field, this means voltage is induced in the slot, and thatnearly no voltage is induced outside the slot, other than what comesfrom the leakage inductance. It is therefore important minimize the endwinding and the winding used for connections as much as possible. Thisis especially an issue for a segmented stator configuration where eachsegment 3 should be independent of the other segments.

This embodiment deals only with a three phase lap winding 21, 22. It canbe applied for a single layer or a double layer winding.

FIG. 41 shows a winding configuration where phase W has a six pole pitchend winding for waste 35. Additional there are three locations 36 wherethere are three coils at the same end winding.

FIG. 42 shows a winding configuration where phase W has a 12 pole pitchend winding for waste 35 and again there are three locations 36 wherethere are three coils at the same end winding.

FIG. 44 shows the simple way, where all the phases are put into thelamination from the same side. The third phase (the phase to the right)needs to have a fourth part 32 of the whole turn, to reach theconnection to the next coil.

In one embodiment of the present invention, a stator segment 3 is havinga set of windings 31, where some windings 31 a, 31 b start from one sideof the stator segment 3 and other(s) 31 c starts from the other side ofthe segment.

An embodiment describes a segment 3 with three phases, where the thirdphase 31 c starts from the other side of the stator segments as thefirst two phases 31 a, 31 b, as shown in FIG. 43.

The third phase winding starting point 40 has to be extended along arear side of the segment 3 (stator lamination) along to reach the otherside where the two windings are having their starting points 40, if sois needed. The third phase output which is connected 37 with the otherphases at the star point 39 or common point 39 needs again be put behindthe stack of stator lamination to reach the other two phases.

FIG. 43 show an optimal winding configuration where the end windingwaste is reduced to twice the iron core length, i.e. the length of aslot, this is mainly only optimal for a generator with a short statorstack, and the generator structure need to allow the winding to gobehind the stator yoke 37. The windings are located so at no end windinglocation are there more than two coils.

FIG. 41 to FIG. 43 shows a setup with just a single winding, the sameprinciple would of course apply in winding configuration with two ormore turns, and also for one or two layers.

FIG. 43 shows an embodiment of the new invention, where the phasewinding goes straight from one to the next without additional turns, thethird phase is put into the lamination from the other side. The thirdphase does not need to have a fourth part of the whole turn, to reachthe connection to the next coil. Therefore the third phase needs to beput behind the stack along two times.

The advantages of the winding configuration shown in FIG. 45, is thatthe last turn that continues at the connection to the next coil, doesnot need to have the fourth part of a whole turn to reach the connectionto part. This applies to all three phases, whereas the configuration inFIG. 44, do need to have the fourth part of a whole turn. In case of alow number of turns and a long segment 3 in the normal direction, butshort lamination stack length, the advantage is bigger, because fractionof coil that is saved becomes even bigger. By reducing the length of thecoil the copper losses are reduced proportionally.

FIG. 44 shows a common winding configuration where the advantagedescribed above is not there. The third phase needs to have a fourthpart 32 of the whole turn also at the last turn to reach the connectionto the next coil.

This can by applied to all segmented machines, either radial flux, axialflux or linear.

An embodiment of the invention relates to a method for assembling agenerator where some windings start from one side of the stator segment3 and other(s) starts from the other side of the segment.

In a method of assembling a stator segment 3 for an electrical machinewith a plurality of windings, where each winding having a windingstarting and ending point, and a stator yoke with a plurality of statorslots 2 for receiving at least one stator winding, the segment 3 ishaving a first side 14 and a second side 15 as in FIG. 3 the methodcomprising the steps of:

-   -   Embedding at least one winding with its starting point 40 at the        first side 14, and its ending point 41 at the first side 14 of        the segment, in one or more stator slots 2, and    -   Embedding at least one other winding having its starting point        40 at the second side 15, and its ending point 41 at the second        side 15 of the segment, in one or more stator slots 2.

In a further embodiment the method of assembling a stator segment 3 alsorelates where the plurality of ending points are connecting at a commonpoint, and where the at least one winding ending at the second sideis/are extended to connect with the other ending points. The at leastone winding ending at the second side 15 may extend along a rear side ofthe segment.

It will be understood that the above description of preferredembodiments is given by way of example only and that variousmodifications may be made by those skilled in the art. The abovespecification, examples and data provide a complete description of thestructure and use of exemplary embodiments of the invention. Althoughvarious embodiments of the invention have been described above with acertain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this invention.

1-15. (canceled)
 16. An electrical machine comprising a plurality ofstator segments, each segment has a plurality of electrical phasewindings embedded in stator slots in a phase sequence, wherein a phaseof a first slot of a segment is different from a phase of a first slotof an adjacent segment.
 17. An electrical machine according to claim 16wherein a sequence of the phase windings is so that the phase windingsform a plurality of electrical phases distributed equally with the samephase angle between the electrical phases.
 18. An electrical machineaccording to claim 16, wherein each of the phase windings in eachsegment is connected in series with the phase winding of a correspondingelectrical phase in the adjacent segment.
 19. An electrical machineaccording to claim 18 wherein a number of windings connected in seriesequals a number of phase windings in each segment times N, wherein N isan integer.
 20. An electrical machine according to claim 19, wherein Ptimes segments forms a first set of electrical phases and Q timessegments forms a second set of electrical phases, wherein the phases ofthe first set is not aligned with the phases of the second set ofelectrical phases.
 21. An electrical machine according to claim 16,wherein a length of at least one of windings in a segment differs from alength of the other windings.
 22. An electrical machine according toclaim 16, wherein the windings are embedded in the slots in a singlelayer.
 23. An electrical machine according to claim 16, wherein thewindings are embedded in the slots in a double layer.
 24. An electricalmachine according to claim 16, wherein each of the windings is aconcentrated wound winding around a single stator tooth of the segment.25. An electrical machine according to claim 16, wherein each of thewindings is wound as a lap winding.
 26. A method of assembling anelectrical machine comprising a plurality of adjacent stator segments,each segment comprising a yoke with a plurality of stator slots, themethod comprising: in a first segment, embedding a plurality ofelectrical phase windings in the stator slots in a phase sequence; in anadjacent segment, embedding a plurality of electrical phase windings inthe stator slots in a phase sequence, connecting the phase windings inthe first segment in series with the phase winding of a correspondingelectrical phase of the adjacent segment so that the phase of the firstslot of a segment is different from the phase of the first slot of anadjacent segment.
 27. The method of assembling an electrical machineaccording to claim 26 wherein a number of windings connecting in seriesequals a number of phase windings in each segment times N, wherein N isan integer.
 28. The method of assembling an electrical machine accordingto claim 26 wherein a length of at least one of windings in a segmentdiffers from a length of the other windings.
 29. The method ofassembling an electrical machine according to claim 26 wherein thewindings are embedded in the slots in a single layer.
 30. The method ofassembling an electrical machine according to claim 26 wherein thewindings are embedded in the slots in a double layer.